The present invention relates to a silver complex diffusion transfer material which comprises combination of a photosensitive material and an image receiving material and in particular, to construction of layer of an image receiving material.
Silver complex diffusion transfer process generally comprises use of a photosensitive material comprising a support and, provided thereon, a silver halide emulsion layer as a photosensitive layer, an image receiving material comprising a support and, provided thereon, an image receiving layer containing physical development nuclei, and a processing solution containing a silver halide solvent. Principle of the silver complex diffusion transfer process is as follows: The silver halide of exposed area of a photosensitive layer which has been subjected to exposure is developed with a developing agent contained in the processing solution or in the photosensitive material and simultaneously the silver halide of unexposed area reacts with the silver halide solvent to produce a soluble silver complex salt, which diffuses to the image receiving material and precipitates on the physical development nuclei to form a silver image.
The silver complex diffusion transfer process based on such principle is widely used for copying of documents and for block copies in plate making.
Important properties required for image receiving materials used in silver complex diffusion transfer process are that silver image produced has a high density (reflection density and transmission density) and is superior in color tone (bluish black tone is generally desired); diffusion transfer speed is high; and the image receiving layer has a sufficient film strength.
Especially, the density of silver image (reflection density and transmission density) is a very important property. In general, copies are required to have a high definition of image and copies of high definition can be obtained when density of the silver image is high. Furthermore, for block copy materials, high density of silver image is desired in order to satifactorily reproduce image qualities (qualities of fine line and dot).
Furthermore, recently the bluish black color tone of silver image has become important property.
Generally, enhancement of silver image density is attained by increasing content of physical development nuclei, but there is the defect in the case of single layer structure that when amount of physical development nuclei is increased, color tone of silver image becomes reddish or the silver image has metallic luster.
This undesirable color tone of silver image cannot be sufficiently improved by using the known blackening agents such as 1-phenyl-5-mercaptotetrazole and this blackening agent has no effect on improvement of metallic luster. If amount of physical development nuclei is decreased, color tone can be improved, but density of silver image much decreases.
The reddish color tone of silver image and the metallic luster occur due to concentration of physical development nuclai to the surface of the image receiving layer and in the case of single layer structure, physical development nuclei are present on the surface of the image receiving layer, too and therefore, most of the diffused silver complex salt is converted to physically developed silver on the surface of the image receiving layer to result in the abovementioned undesirable color tone of silver image or metallic luster.
As a general means employed in order that physical development nuclei are not present on the surface of the image receiving material, there is a method of using two or more layers as layer construction of the image receiving material and providing a layer containing no physical development nuclei (hereinafter referred to as "uppermost layer") on a layer containing physical development nuclei (hereinafter referred to as "image receiving layer"). This method is disclosed, for example, in Japanese Patent Kokai No. Hei 1-94344.
By providing the uppermost layer, physical development nuclei are not present on the surface and hence, physically developed silver is not concentrated on the surface and metallic luster of silver image can be inhibited.
However, the conventionally employed uppermost layer can inhibit generation of metallic luster, but there are problems that color tone of silver image is inferior or transfer density is not sufficient.
According to further investigation, it has been found that when the image receiving layer of such image receiving material is hardened with a hardener contained therein, silver image becomes continuous silver (metallic silver) at the interface between the image receiving layer and the colloid layer containing no development nuclei and thus, specular silver is formed and so-called Newton's ring is generated between the specular silver and the layer thereon due to interference of light, resulting in considerable deterioration of image quality.